1. Field of the Invention
This invention relates to the plasma etch chamber of a plasma etching apparatus provided with a protective conductive coating formed on the inner metal surfaces of the chamber and a method of forming such a protective coating.
2. Description of the Related Art
The plasma etch chamber of apparatus used for plasma etching of materials such an semiconductor wafers is usually constructed using metal such as aluminum for the etch chamber walls. When plasma etching is used with certain types of gases, such as halogen gases, e.g., chlorine, corrosion of the metal walls can occur. This has necessitated the formation of a protective coating on the metal surfaces facing the chamber, i.e., the inner surfaces of the chamber walls.
When aluminum constitutes the metal used for the chamber walls, conventionally the aluminum is anodized and the resulting aluminum oxide coating provides the necessary chemical protection against corrosive attack of the aluminum by the halogen gases.
However, while anodizing the inner aluminum surfaces of the plasma etch chamber at least partially solves the problem of chemical attach by the reactive gases used in the etch chamber, such anodizing, in turn, creates other problems. Being an insulator, the presence of the anodized coating on the etch chamber walls results in poor plasma electrical contact to the grounded metal chamber surface which leads to arcing, high plasma potential, and poor grounding, leading, in turn, to problems of process repeatability and process control. Furthermore, such electrical problems can, in turn, lead to further chemical corrosion problems since the plasma, in seeking out ground, often concentrates on any cracks in the insulative coating which can lead to chemical corrosion concentrated at such locations.
It would, therefore, be desirable to provide protection means against chemical attack to the inner metal surfaces of the etch chamber of a plasma etching apparatus without interfering with the electrical functions of the plasma etching apparatus. Furthermore, such protection means must not in any way degrade any integrated circuit devices formed or to be formed on the semiconductor wafer being etched in the etch chamber.